Mems mirror with drive rotation amplification of mirror rotation angle

ABSTRACT

A micro-electro-mechanical system (MEMS) mirror device includes a mirror coupled to a rotating frame by a first torsional hinge along a rotational axis. The rotating frame has a body that defines a frame opening, and a group of rotational teeth extending from the body. A first bonding pad is located in the frame opening and coupled to the rotating frame by a second torsional hinge along the rotational axis. A second bonding pad is coupled to the rotating frame by a third torsional hinge along the rotational axis.

FIELD OF INVENTION

This invention relates to micro-electro-mechanical system (MEMS)devices, and more particularly to MEMS scanning mirrors.

DESCRIPTION OF RELATED ART

Various electrostatic comb actuator designs for MEMS scanning mirrorshave been proposed. The extensive applications of these devices includebarcode readers, laser printers, confocal microscopes, projectiondisplays, rear projection TVs, and wearable displays (e.g., microdisplays). For these applications, the MEMS scanning mirrors typicallyneed to have a great range of rotation. Thus, what is needed is a MEMSscanning mirror that has a great range of rotation.

SUMMARY

In one embodiment of the invention, a micro-electro-mechanical system(MEMS) mirror device includes a mirror coupled to a rotating frame by afirst torsional hinge along a rotational axis. The rotating frame has abody that defines a frame opening, and a group of rotational teethextending from the frame body. A first bonding pad is located in theframe opening and coupled to the rotating frame by a second torsionalhinge along the rotational axis. A second bonding pad is coupled to therotating frame by a third torsional hinge along the rotational axis.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A illustrates a perspective cut-away view of a MEMS mirror devicein one embodiment of the invention.

FIG. 1B illustrates a perspective cut-away view of a lower layer in theMEMS mirror device of FIG. 1A in one embodiment of the invention.

FIGS. 2 and 3 illustrate partial top views of the layers in the MEMSmirror device of FIG. 1A along a vertical line of symmetry in oneembodiment of the invention.

FIG. 4 illustrates a cross-sectional view of the MEMS mirror device ofFIG. 1A in one embodiment of the invention.

FIGS. 5 and 6 illustrate partial top views of the layers in a MEMSmirror device along a vertical line of symmetry in another embodiment ofthe invention.

Use of the same reference numbers in different figures indicates similaror identical elements.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1A partially illustrates a MEMS mirror device 100 along a verticalline of symmetry 103 in one embodiment of the invention. Device 100includes an upper layer 102 bonded to but electrically insulated from alower layer 202 (shown more clearly in FIG. 1B) by an insulation layer105. Components on upper layer 102 and lower layer 202 can be formedfrom semiconductor wafers using semiconductor processing techniques.

Referring to FIG. 2, upper layer 102 includes a mirror 104 connected bya torsional hinge 106 to a first end of a rotating frame 108 along arotational axis 110. A second end of rotating frame 108 is connected bya torsional hinge 112 to a bonding pad 114 along rotational axis 110.

In one embodiment, mirror 104 defines a slot 115 that divides itselfinto a tab portion 104A that is connected to a reflector portion 104Babove and below slot 115. In this embodiment, torsional hinge 106 isconnected between tab portion 104A and rotating frame 108.

Rotating frame 108 is a beam-like structure having a body that definesone or more frame openings 116 (only one is illustrated for clarity).Each frame opening 116 accommodates a bonding pad 117. Opposing sides ofeach bonding pad 117 are connected by torsional hinges 118 and 119 torotating frame 108 along rotational axis 110.

Rotating frame 108 has two opposing sides 108A and 108B relative torotational axis 110. Rotational comb teeth 120 (only one is labeled forclarity) extend from side 108A while rotational comb teeth 122 (only oneis labeled for clarity) extend from side 108B.

Rotating frame 108 also has beams 108C and 108D protruding from one endof rotating frame 108 to sandwich torsional spring 106. Rotational combteeth 120 extend from beam 108C while rotational comb teeth 122 extendfrom beam 108D. Similarly, rotating frame 108 has beams 108E and 108Fprotruding from the other end of rotating frame 108 to sandwichtorsional spring 112. Rotational comb teeth 120 extend from beam 108Ewhile rotational comb teeth 122 extend from beam 108F. Note that sides108A and 108B may extend further outward than beams 108C, 108D, 108E,and 108F to provide room to form bonding pads (e.g., bonding pad 117)within rotating frame 108 that would properly mount to anchoring pads(e.g., anchoring pad 218) below.

Bonding pads 124 and 126 are formed on opposing sides of rotating frame108. Stationary comb teeth 128 (only one is labeled for clarity) extendfrom bonding pad 124 toward rotating frame 108 while stationary combteeth 130 (only one is labeled for clarity) extend from bonding pad 126toward rotating frame 108. When rotation frame 108 is level (as shown),stationary comb teeth 128 and rotational comb teeth 120 areinterdigitated while stationary comb teeth 130 and rotational comb teeth122 are interdigitated. To match rotational comb teeth 120, stationarycomb teeth 128 are staggered with two side sections that extend closerto rotational axis 110 than a middle section. Stationary comb teeth 130are also be staggered to match rotational comb teeth 122.

In one embodiment, the components of upper layer 102 are formed byetching a semiconductor wafer.

Referring to FIG. 3, lower layer 202 includes an anchoring pad 218 ontowhich bonding pad 117 (FIG. 2) is mounted. Lower layer 202 furtherincludes an anchoring pad 206 having a horizontal sections 224 ontowhich bonding pad 124 (FIG. 2) is mounted, a horizontal section 226 ontowhich bonding pad 126 (FIG. 2) is mounted, and a vertical section 214onto which bonding pad 114 is mounted.

Stationary comb teeth 228 extend from horizontal section 224 towardrotational axis 110. Stationary comb teeth 228 are staggered to matchrotational comb teeth 120. Similarly, stationary comb teeth 230 extendfrom horizontal section 226 toward rotational axis 110. Stationary combteeth 230 are also staggered to match rotational comb teeth 122.Stationary comb teeth 228 and rotational comb teeth 120 areinterdigitated at least when rotating frame 108 rotates in one direction(e.g., as shown in FIG. 4). Conversely, stationary comb teeth 230 androtational comb teeth 122 are interdigitated at least when rotatingframe 108 rotates in the opposite direction.

Lower layer 202 further includes an optional supporting rib structure240 onto which mirror 104 (FIG. 2) is mounted. Rib structure 240includes vertical crossbeams 242 and horizontal crossbeams 244 (only oneof each is labeled for clarity). When mounted to rib structure 240,mirror 104 has less dynamic deformation and the optical resolution ofdevice 100 is increased. Rib structure 240 is separated from theremainder of lower layer 202 by a gap 204.

In one embodiment, the components of lower layer 202 are formed byetching a semiconductor wafer so all the appropriate components arestructurally supported by a floor 208. The etching process also formsgap 204 around rib structure 240 to accommodate the rotation of mirror104 (FIG. 2).

FIG. 4 is now used to explain the design benefits of device 100 in oneembodiment. Typically stationary comb teeth 228/230, anchoring pad 206(FIG. 3), anchoring pad 218 (FIG. 3), and gap 204 (FIG. 3) are formed bythe same etching step. As the dimensions of stationary comb teeth228/230 are much smaller than the dimensions of the other components,floor 208 around anchoring pad 218 is etched at a much faster rate thanthe spacing between stationary comb teeth 228. Thus, the etching processis stopped before floor 208 is etched through and anchoring pad 218becomes unsupported. However, when the etching process is stopped, thedepth 302 of the spacing between stationary comb teeth 228/230 is muchshallower than the depth 304 of floor 208. This prevents rotational combteeth 120/122 from reaching a rotation depth 306 required for someapplications of mirror 104. On the other hand, gap 204 is etched throughto provide for the angle rotation of the mirror.

To address this challenge, rotating frame 108 (FIG. 2) is torsionally,instead of fixedly, connected to mirror 104 (FIG. 2) by torsional hinge106 (FIG. 2). As rotating frame 108 rotates, its rotational motion istransferred to mirror 104 by torsional hinge 106. Torsional hinge 106 inturn amplifies the rotational motion so that mirror 104 is rotated at agreater angle. The exact amplification of mirror 104 can be determinedby studying the vibration mode shape through computer simulation ofdevice 100. For example, to amplify the rotational amplitude of mirror104 relative to the rotational amplitude of rotating frame 108, thestiffness of hinge 106 need to be reduced.

Device 100 can be operated in a variety of fashion. In one embodiment,rotational comb teeth 120 and 122 are coupled via bonding pad 114 toreceive a reference voltage (e.g., DC). Stationary comb teeth 128 and130 are coupled via bonding pads 124 and 126, respectively, to receivean oscillating voltage with a steady voltage bias (e.g., an AC+DCvoltage). Stationary comb teeth 228 and 230 are coupled via bonding pad206 to receive an oscillating voltage (e.g., an AC voltage source). Thetwo oscillating voltages have a phase shift of 180 degrees. Thus, asteady (e.g., DC) voltage difference between rotational comb teeth120/122 and stationary comb teeth 128/130 changes the natural frequencyof device 400, whereas oscillating (e.g., AC) voltage differencesbetween rotational comb teeth 120/122 and stationary comb teeth128/130/228/230 oscillate the mirror at the desired scanning frequencyand at the desired scanning angle. The DC voltage difference betweenrotational comb teeth 120/122 and stationary comb teeth 128/130 isadjusted by adjusting the steady voltage bias of the oscillating voltageprovided to stationary comb teeth 128 and 130.

FIGS. 5 and 6 partially illustrate an upper layer 402 and a lower layer502 of another MEMS mirror device in one embodiment of the invention.This mirror device is similar to mirror device 100 (FIG. 1A) but for thefollowing.

Referring to FIG. 5, layer 402 is similar to layer 102 except thatmirror 104 is replaced with a mirror 404. Like mirror 104, mirror 404 isconnected by torsional hinge 106 to a first end of rotating frame 108along rotational axis 110. However, mirror 404 further defines anopening 406 to accommodate a bonding pad 410. Bonding pad 410 isconnected by a torsional hinge 412 to mirror 404 along rotational axis110.

Referring to FIG. 6, layer 502 is similar to layer 202 except thatadditional anchoring pads 510A and 510B are formed in lower layer 502 tosupport bonding pad 410.

As described above, mirror 404 is connected by torsional hinge 106 torotating frame 108 and by torsional hinge 412 to bonding pad 410. Thestiffnesses of hinges 106 and 412 are adjusted to control the rotationalamplitude of mirror 404. For example, to amplify the rotationalamplitude of mirror 404 relative to the rotational amplitude of rotatingframe 108, the stiffness of hinge 412 should be reduced and thestiffness of hinge 106 should be made relatively larger. Conversely, todampen the rotational amplitude of mirror 404 relative to the rotationalamplitude of rotating frame 108, the stiffness of hinge 412 should beincreased and the stiffness of 106 should be made relatively smaller.The exact amplification and dampening rotational amplitude of mirror 404is also related to the structure inertia distribution and thestiffnesses of the other hinges, which can be determined by studying thevibration mode shape through computer simulation of the device. Thedevice can be operated in the same manner as device 100.

Various other adaptations and combinations of features of theembodiments disclosed are within the scope of the invention. Numerousembodiments are encompassed by the following claims.

1. A micro-electro-mechanical system (MEMS) mirror device, comprising: amirror; a rotating frame defining a frame opening; a plurality ofrotational teeth extending from the rotating frame; a first torsionalhinge coupling the mirror and a first end of the rotating frame along arotational axis; a first bonding pad in the frame opening; a secondtorsional hinge coupling the rotating frame and the first bonding padalong the rotational axis; a second bonding pad; and a third torsionalhinge coupling a second end of the rotating frame and the second bondingpad along the rotational axis.
 2. The MEMS minor device of claim 1,wherein the mirror defines a slot that divides the mirror into areflector portion and a tab portion coupled by the first torsional hingeto the first end of the rotating frame.
 3. The MEMS mirror device ofclaim 1, further comprising: a first anchoring pad onto which the firstbonding pad is mounted; and a second anchoring pad onto which the secondbonding pad is mounted.
 4. The MEMS mirror device of claim 1, furthercomprising: a third bonding pad; and a plurality of stationary teethextending from the third bonding pad to be interdigitated with theplurality of rotational teeth when the rotating frame is in a firstposition.
 5. The MEMS mirror device of claim 4, further comprising: afirst anchoring pad onto which the first bonding pad is mounted; asecond anchoring pad, comprising: a first section onto which the secondbonding pad is mounted; a second section onto which the third bondingpad is mounted; and another plurality of stationary teeth extending fromthe second section to be interdigitated with the plurality of rotationalteeth when the rotating frame is in a second position.
 6. The MEMSmirror device of claim 5, further comprising: a supporting structurecomprising crossbeams, the mirror being mounted on the supportingstructure.
 7. The MEMS mirror device of claim 6, wherein: the mirror,the rotating frame, the first bonding pad, the second bonding pad, thefirst torsional hinge, the second torsional hinge, the third torsionalhinge, the plurality of rotational teeth, and the plurality ofstationary teeth are part of a first layer of the device; and the firstanchoring pad, the second anchoring pad, and the supporting structureare part of a second layer of the device onto which the first layer ismounted.
 8. The MEMS mirror device of claim 1, wherein the mirrordefines a minor opening, the device further comprising: a third bondingpad in the mirror opening; and a fourth torsional hinge coupling themirror and the third bonding pad along the rotational axis.
 9. The MEMSmirror device of claim 8, further comprising: a first anchoring pad ontowhich the first bonding pad is mounted; a second anchoring pad ontowhich the second bonding pad is mounted; and a third anchoring pad ontowhich the third bonding pad is mounted.
 10. The MEMS mirror device ofclaim 9, further comprising: a fourth bonding pad; and a plurality ofstationary teeth extending from the fourth bonding pad to beinterdigitated with the plurality of rotational teeth.
 11. The MEMSmirror device of claim 10, further comprising: a first anchoring padonto which the first bonding pad is mounted; a second anchoring pad,comprising: a first section onto which the second bonding pad ismounted; a second section onto which the fourth bonding pad is mounted;and another plurality of stationary teeth extending from the secondsection to be interdigitated with the plurality of rotational teeth; athird anchoring pad onto which the third bonding pad is mounted.
 12. TheMEMS mirror device of claim 11, further comprising: a supportingstructure comprising crossbeams, the mirror being mounted on thesupporting structure.
 13. The MEMS mirror device of claim 12, wherein:the mirror, the rotating frame, the first bonding pad, the secondbonding pad, the third bonding pad, the fourth bonding pad, the firsttorsional hinge, the second torsional hinge, the third torsional hinge,the fourth torsional hinge, the plurality of rotational teeth, and theplurality of stationary teeth are part of a first layer of the device;and the first anchoring pad, the second anchoring pad, the thirdanchoring pad, the supporting structure and said another plurality ofstationary teeth are part of a second layer of the device onto which thefirst layer is mounted.
 14. A method for operating amicro-electro-mechanical system (MEMS) mirror device, comprising:coupling a mirror and a rotating frame with a first torsional hingealong a rotational axis; coupling the rotating frame to a bonding padwith a second torsional hinge along the rotational axis; providing afirst voltage to a plurality of rotational teeth extending from therotating frame; providing a second voltage to a plurality of stationaryteeth, the plurality of stationary teeth being interdigitated with theplurality of rotational teeth when the rotating frame is in a firstposition; wherein: an oscillating voltage difference between theplurality of rotational teeth and the plurality of stationary teethoscillates the rotating frame about the rotational axis; and the firsttorsional hinge transfers a rotational motion of the rotating frame tothe mirror so the mirror rotates at a different angle than the rotatingframe.
 15. The method of claim 14, wherein the first voltage comprises asteady voltage and the second voltage comprises an oscillating voltageand a steady voltage bias, a steady voltage difference between theplurality of rotational teeth and the plurality of stationary teethchanging a natural frequency of the device.
 16. The method of claim 15,further comprising: providing a third voltage to another plurality ofstationary teeth, said another plurality of stationary teeth beinginterdigitated with the plurality of rotational teeth when the rotatingframe is in a second position.
 17. The method of claim 16, wherein thethird voltage comprises another oscillating voltage out of phase withthe second voltage, wherein another oscillating voltage differencebetween the plurality of rotational teeth and said another plurality ofstationary teeth oscillates the rotating frame about the rotationalaxis.
 18. The method of claim 14, further comprising: coupling themirror and another bonding pad with a third torsional hinge along arotational axis.
 19. The method of claim 14, further comprising:supporting the mirror by mounting the mirror onto a structure havingcrossbeams.